Conventionally, since the grounding poles have been buried into the earth, especially into the earth with poor conductivity such as a sandy soil and a rocky stratum without taking into consideration the material of the grounding pole, length of the pole, necessity of a connector for the grounding pole and others, it has been difficult to maintain the initial grounding resistance for a long period of time due to rust of the connected part, corrosion of the grounding pole. When a momentary large current such as lightning current flows into the grounding pole which employs iron, the impedance becomes large and the resistance also becomes large due to rust on the grounding pole and therefore it will be impossible to discharge such large current into the earth in safety. In other words, the protection relays have been burnt, safety communication lines have been discontinued and precision machines have been burnt, thus the protection and maintenance of electric circuits have been greatly affected.